Beverage dispensing systems commnonly use an internal ice bank to cool the beverage to a predetermined temperature before the beverage is served to a customer. An example of a known beverage dispensing system with an internal ice bank is shown in commonly-owned U.S. Pat. No. 5,022,233 to Kirschner, et al., entitled "Ice Bank Control System for a Beverage Dispenser." As is shown in this reference and in FIG. 1 herein, a beverage dispenser 10 may use a mechanical refrigeration system 12. The refrigeration system 12 includes an ice water bath tank 14, a plurality of evaporator coils 16 positioned in the tank 14 to build an ice bank 17, a plurality of syrup cooling coils 18, a plurality of water cooling coils 19, an agitator 20, an agitator motor 22, and a compressor or an evaporator system including a compressor motor 24 and a control box 26 housing an ice bank control system 28.
In use, syrup and water passing through the syrup coils 18 and the water coils 19 are chilled by the ice of the ice bank 17. The ice is created by the compressor system removing heat from the water in the ice water bath tank 14. The compressor system may use the plurality of evaporator coils 16 as is shown, one or more evaporator plates of roll-bond construction, or other conventional means of removing heat. The evaporator coils 16 or the evaporator plates are powered by the compressor motor 24. Operation of the compressor motor 24 is controlled by the ice bank control system 28. The ice bank control system 28 monitors the growth of the ice bank 17 so as to run the compressor motor 24 until a predetermined amount of ice has developed. If too much ice grows, the syrup and water coils 18, 19 may freeze. After the compressor motor 24 is shut down, the ice bank control system 25 may again turn on the compressor motor 24 after a predetermined interval to prevent the ice bank 17 from deteriorating. In one embodiment, this reference discloses the use of a thermistor sensing element 30 positioned at a predetermined distance from the evaporator coils 16. The ice bank control system 25 therefore turns the compressor motor 24 off when the sensor 30 detects the presence of a predetermined amount of ice. U.S. Pat. No. 5,022,233 is incorporated herein by reference.
A similar ice bank control system is shown in commonly-owned U.S. Pat. No. 4,4907,179, entitled "Ice Bank Control System for Beverage Dispenser." This reference uses a pair of sensors to determine the growth of the ice bank at predetermined positions spaced from the evaporator coils. U.S. Pat. No. 4,4907,179 is also incorporated herein by reference. Other known ice bank devices use various types of mechanical and electrical sensors, oscillation frequencies, and even optics to detect the growth of ice. In each of these systems, the compressor runs and promotes the growth of ice within the ice bank until the control system determines that a sufficient amount of ice has been made. At that point, the control system turns the compressor off until a predetermined length of time elapses, the ice bank shrinks to a predetermined size, or some other predetermined variable is reached.
Although the purpose of an ice bank detector is to control the refrigeration system such that as much ice as possible grows without freezing the product cooling lines, known detectors only detect the growth of ice at one point in the ice bank. Such detectors, therefore, are not always reliable when, for example, ice bank erosion occurs or when the refrigeration units are improperly charged. These conditions can result in uneven ice growth across the ice bank. For example, FIG. 2 shows the typical shape of an ice bank 50 with a low or an uneven refrigeration charge. As is shown, significant ice growth occurs at the bottom of the ice bank 50 with a much smaller amount of ice growth at the top. The detector 60, however, is positioned at the top of the ice bank 50 and would not detect the ice at the bottom of the ice bank 50. The result is that the compressor would continue to run and cause the ice bank 50 in the bottom of the tank to freeze the product lines 70 well before the detector 60 sensed the presence of the ice bank 50.
What is needed, therefore, is an ice bank detector that monitors the growth of ice across a significant portion of the entire ice bank. Such a device would accurately determine the growth of ice throughout the ice bank regardless of uneven ice growth or erosion. Such a detector must accomplish these goals in a reliable and cost effective manner.